1. Field of the Invention
The present invention relates to an implantable electrode lead and, more particularly, to an implantable electrode lead to be implanted in body tissue, which improves the repetition durability of the lead body of the electrode lead in the body tissue when used generally together with a cardiac pacemaker or implantable defibrillator and which can reduce the mechanical stress applied by the lead body onto the body tissue because of its softness.
2. Description of the Related Art
Many types of implantable electrode leads used together with a cardiac pacemaker or implantable defibrillator are conventionally known. Generally, an electrode lead is constituted by at least one electrode, an electrical connector, and a lead body, and is used as an implantable electrode lead. The electrode electrically stimulates the heart or senses electrical cardiac activity in one or both of the chambers of the heart. The electrode lead is electrically connected to the cardiac pacemaker or implantable defibrillator through the electrical connector. The lead body is arranged between the electrode and electrical connector, and is formed of an electrical conductor and a bio-compatible electrically insulating cover. The electrical conductor transmits an electrical signal between the electrode and the cardiac pacemaker or implantable defibrillator.
In a transvenously used implantable electrode lead, the electrode and part of the lead body are inserted in the heart and vein. The lead body outside the vein and the electrical connector are extended to a connection housing for the cardiac pacemaker or defibrillator and connected to it.
Currently, in the lead body of a bipolar implantable electrode lead, a coaxial structure constituted by two types of conductive coils having different pitch diameters (mean diameters), an insulating sheath located between the two conductive coils, and a sheath located on the outermost surface of the lead body is the main stream.
According to another lead structure, a sheath is formed on the outer surface of an insulating parallel-wound coil on which a conductive wire with insulating coating is wound with the same pitch diameter (mean diameter).
Generally, in a conductive coil used in an implantable electrode lead, since the conductive wire is helically wound, when the lead body deforms, the internal stress of the conductive wire is reduced. It is known that the larger the spring index (D/d), the larger this internal stress reducing effect where D is the pitch diameter (mean diameter) of the conductive coil, d is the diameter of the conductive wire, and d and D are constant.